The present invention generally relates to machines for use in the maintenance of a railroad track, and more particularly to a toggle slide-plate for use in a railroad spike-pulling machine.
Maintenance of railroad tracks and the periodic replacement of wooden railroad ties or worn rails or rail segments require the removal of spikes from the ties and corresponding tie plates to separate the rails from the ties and position the new ties. In the present application, “spikes” will be understood to mean rail fasteners including standard “cut” spikes, hairpin spikes, screw spikes, and other equivalent rail fasteners. Railroad spike-pulling machines, of the type disclosed in commonly assigned U.S. Pat. No. 4,538,793, incorporated by reference, accomplish the removal of these spikes with a gripping or clamping assembly generally including a pair of reciprocating jaws, where each jaw is located on a corresponding side of the rail. Each jaw also has a claw member at a distal jaw end that is operable for gripping the head of the spike. Once the claw member has gripped the spike, a mechanical linkage lifts the jaws upward so that the spike is pulled from the tie and the tie plate. The mechanical linkage for lifting the clamping assembly generally includes fluid power cylinders, as known in the art.
One problem that arises during operation of these assemblies is that as the machine travels along the track, the jaws are subjected to a perpendicular force. This force can cause the jaws to twist, misaligning them and preventing the claw members from properly gripping the tie spikes.
To address this potential problem, supporting connecting links were developed to maintain the alignment between the jaws and prevent them from twisting. A lower end of each pair of connecting links is attached by brackets to the pivotable intermediate section of the jaws. A hydraulic cylinder is configured to maintain a connection between the lower ends of the connecting links, and helps to prevent the jaws from twisting. An upper end of each of the connecting links is connected to a pair of spaced apart guide slots which define the travel limits of the links during movement of the jaws.
The opposite ends of the guide slots are generally supported by a plate assembly. Current plate assemblies generally include a pair of endplates supported for vertical movement by a mid-plate. The opposite ends of the mid-plate are slidably housed in channels in a supporting frame member. The mid-plate slides up and down the channels as the jaws move away and towards the spike, respectively. One problem that arises with these plate assemblies is that the ends of the mid-plate become worn down through sliding on the channels, requiring the plate to be replaced. To replace the plate assembly, the connecting links must be unscrewed from the endplates, and then the endplates must be removed from the mid-plate, so the mid-plate can be removed from the machine.
However, this process can be very time consuming because the plate assembly is virtually inaccessible after assembly of the machine, thus reducing operating efficiency. Furthermore, replacement of the mid-plate requires the use of special tools that can access the plate assembly. Also, the entire mid-plate needs to be replaced in current plate assemblies, even though only the ends of the mid-plate have been worn down. Therefore, replacement of the entire mid-plate is not cost-effective. In addition, during operation of the tool, the plurality of welds that secure the endplates to the mid-plate can become loosened, reducing the effectiveness of the plate assembly by permitting twisting of the jaws.
Therefore, there exists a need for a plate assembly that can be easily replaced after the ends of the mid-plate become worn down. There also exists a need for a plate assembly where the ends of the mid-plate can be replaced without the use of special tools and without the need to disassemble the spike-pulling machine. Also, there exists a need for a method of replacing the worn down ends of the mid-plate without the need to replace the entire mid-plate. Finally, there exists a need for a plate assembly that is accessible after assembly of the machine, so that adjustments can be easily made.